The primary commercial method to date of preparing organopolysiloxanes is by the hydrolysis of the corresponding chlorosilanes. This method gives excellent yields of both cyclic and linear polysiloxanes but it involves handling aqueous hydrochloric acid. Since it is necessary to convert the hydrochloric acid to methyl chloride, the process is more complicated than is desired. It would be highly desirable, therefore, to be able to react the chlorosilanes directly with a material producing methyl chloride and thus avoiding the handling of aqueous acid.
U.S. Pat. No. 4,108,882 discloses and claims such a method. This involves reacting dimethyldichlorosilane or trimethylmonochlorosilane with methanol in the presence of certain quaternary ammonium catalysts. The products are primarily cyclic polysiloxanes and methyl chloride which contains a very low percentage of dimethyl ether.
The primary objective of said patent was to produce cyclic polydimethylsiloxanes as set forth in column 1, line 45. Therefore, the patent stresses the use of atmospheric pressure. However, in column 38, the patentee also says that the reaction "may be carried out under conditions below, at or above atmospheric." There is no teaching in the patent that super atmospheric pressure would change the product balance between cyclic and linear siloxanes. In fact, the clear import is that no change would occur. Thus, while carrying out the process at super atmospheric pressure would constitute an infringement of the claims of said patent, there is nothing in the patent to indicate that one seeking a high yield of linear polysiloxanes by reacting methylchloride with dimethyldichlorosilane would find the answer by operating at super atmospheric pressure.
In commercial operation it is often desirable to produce a high proportion of linear siloxanes at the same time that cyclic siloxanes are being produced. This is true because many siloxane products require linear siloxane raw materials.
The object of this invention is to produce a mixture of linear and cyclic siloxanes containing a high proportion of linear materials without sacrificing the benefits of the aforesaid patent; namely, high methyl chloride production with low dimethyl ether content and excellent yields of siloxane product.